Tar sands are geological formations located in subterranean veins capped by impermeable rock, leading to a natural compatibility to form a subterranean pressurized steam chamber to heat up the tar sand veins and mobilize the heavy oil. In this specification “heavy oil” refers to bitumen that requires energy to separate from the geological phase and flow to the surface in contrast to light oil that is free to flow and naturally pressurized and so only requires a direct path to the surface to be extracted.
The U.S. Pat. No. 4,334,485 issued to Roger M. Butler discusses a method to continuously steam tar sand veins via a horizontal injector well running parallel over a horizontal producer well near the bottom of the vein that pump up to the surface the heavy oil flowing into it by gravity. This is the process now known as SAGD in the industry. Butler proposes an initial phase where steam is injected in both wells to heat up the zone in between and mobilize the heavy oil in it, called the conditioning phase which insures proper flow into the producer. Once, this “pool” of liquefied heavy oil covers the producer well, the injection of steam into it is stopped and the heavy oil that flows into it is pumped to the surface naturally or artificially by a using pump or gas lift. Steam is continuously injected by the injector well over the producer well creating a steam chamber that grows up in the tar sand vein, mobilizing trapped heavy oil that then flows down to a producer pool by gravity.
The extraction of heavy oil from tar sands is challenging both from a technological and a commercial perspective. Many operational parameters need to be properly set to optimize the rate of oil recovery. Examples of operating conditions include: the rate at which heavy oil is recovered and the temperature and amount of steam injected in the steam chamber, among many others. However, the gathering of information about the conditions in the subterranean reservoir is difficult. In practice, an SGAD installation provides the operator with a few data points only. While the data points are useful, in most cases they are not sufficient to make clear choices about the operational conditions to be implemented.
Accordingly there is a need in the industry to provide novel techniques and devices to provide a better understanding of the conditions occurring in a subterranean reservoir from which a hydrocarbon based fluid is extracted.